Phil,
Some parts are not hermetically sealed, especially relays which the nib (vent) should be removed after in-line cleaning. Once the nib is removed, reworking the board becomes a challenge as the part cannot go into the cleaner again, yet localized "ionic distribution" isn't an acceptable alternative, either. We have recently seen an increase in entrapment in electrolytic cap marking sleeves (shrink tube). I'm still working on this one and it's a costly nuisance since these assemblies are conformal coated, hence shelf time won't desiccate them.
"We are not alone"
Ed Popielarski
Engineering Manager
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Oak Harbor, Wa. 98277
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-----Original Message-----
From: TechNet [mailto:[log in to unmask]] On Behalf Of Nutting, Phil
Sent: Thursday, July 31, 2014 7:38 AM
To: [log in to unmask]
Subject: [TN] component failures due to post wave/reflow washing
Over the past years we have had relays, optos and pots fail due to corrosion being found inside the parts after post soldering wash. The quick solutions have been to use other manufacturer's parts or install after wash with hand solder "no-clean" cored flux. One manufacturer said it was because of halides in the flux. Our primary CM's and our flux contains halides, but we haven't seen as many failures with in-house processed PTH boards as with CM built boards. Recent pot failures have been explained by component manufacturers as too much wash pressure or bad flow direction from the wash jets. Opto failures were similarly diagnosed.
Our in-house process, all PTH, is foam flux with OA flux, wave solder with 63/37 or SC995e followed by a closed loop DI wash with no chemicals. This has been a great process since 2006 when we switched from a no-clean foam flux, 63/37 wave and terpene/alcohol wash to our listed system above.
We do not dictate flux/wash process to our CMs, but we do specify cleanliness to J-STD-001 C-22 using the 1.56 ėgm / cm2 NaCl equivalent contamination value. Forcing the CM to change fluxes for our product met great resistance and added cost so no change in flux was made.
Our business is high voltage from 30 kV to 240 kV so clean with NO residue is very important. The DI wash has provided that in-house.
We are using different CMs going forward, but not necessarily for this reason.
Is this a problem unique to us or do other suffer from similar problems?
Phil Nutting | HVP Development Engineer | Excelitas Technologies Corp
Lab: +1 978.224.4332 | Office: +1 978.224.4152
35 Congress St, Salem, MA 01970 USA
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www.excelitas.com<http://www.excelitas.com/>
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